I’m inclined to think the JT610 crew had to handle a more difficult and stressing false Stall warning and recovery situation, which is the same between the 737NG and the 737 MAX. In isolation, this should be easy to spot and the correct action (Cut out the trim as described below) could be taken in relative calmness.
#BOEING 747 FCOM MANUAL SIMULATOR#
This action is not described in the 737NG FCOM and might be the reason why the bulletin is restricted to the 737 MAX type, which has implemented this to increase longitudinal stability for this type.Īny such Automatic trim action which doesn’t makes sense has the feel of a runaway pitch trim which is a very common emergency simulator training scenario.
#BOEING 747 FCOM MANUAL MANUAL#
The angle of attack is also used to control an Automatic trim action during manual flight to gradually relieve the pilot of any constant stick forces. To combat such a situation, the 737 (as other airliners) has an implemented Stall warning and recovery system. If this angle is too large, the wing stalls (loses lift). The AOA sensor measures how large the angle is between the approaching air and the wings pitch incidence. Whether the Alpha Vane or some other part of the system generated this false reading is not known. In the crash flight, the problem seems to have affected the Angle Of Attack information. The actions to correct the problem after the prior flight seem not to have worked. The flight crew prior to JT610 identified the unreliability to the captain’s displays, which should mean the left ADIRU with sensors had a problem. Exactly what’s the root cause of this unreliable information (sensors, computer, communication to displays…) is not known. We interpret this as one of the primary ADIRU systems has delivered unreliable airspeed. The Indonesian crash investigators have said the 737 MAX involved in the crash has flown with unreliable airspeed information in the last four flights. Boeing 737NG and MAX primary air data sensors with processing systems. Figure 1 shows the flight control surfaces which exist on the 737NG and MAX.įigure 3. To explain how a false AOA value can affect the aircraft, we need to understand the 737 flight control system for the pitch function. This might have been made more difficult by a simultaneous false reading of airspeed from the same system (one of three systems generating airspeed on the aircraft). In the case of the Lion Air Flight JT610 the correct identification and action upon an incorrect AOA sensor information seem not to have been made. The system and its sensors have not been changed since the introduction of the 737NG in 1998.
These procedures and the sensor system triggering them has stayed the same since 20 years as far as we understand. The Flight Crew Operations Manual (FCOM) bulletin from Boeing reminds operators that the existing procedures are the correct actions to be taken if an aircraft encounters a false stall warning and flight control recovery triggered by a faulty Angle Of Attack signal. The FAA has alerted foreign airworthiness authorities who oversee operators that use the 737 MAX of the agency’s action. The FAA continues to work closely with Boeing, and as a part of the investigative team on the Indonesia Lion Air accident, may take further appropriate actions depending on the results of the investigation. Operators have three days to revise the AFM. The AD orders operators to revise the airplane flight manual (AFM) to give the flight crew horizontal stabilizer trim procedures to follow under certain conditions. These erroneous inputs can potentially make the horizontal stabilizers repeatedly pitch the nose of the airplane downward, making the aircraft difficult to control. “ The FAA has issued an Emergency Airworthiness Directive (AD) that addresses possible erroneous angle of attack (AOA) inputs on Boeing 737 Max aircraft. The Federal Aviation Administration has today issued an Airworthiness Directive for the 737-8 and -9: Below, we try to bring some clarity and perspective into what is sometimes sensational headlines out of a minimum of facts. We have read the Boeing bulletin, what has been issued from the Indonesian crash investigators and the FAA, and what has been discussed in media. Source: Wikipedia.īoeing’s 737 AOA sensors and how it affects the aircraft
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